1. Field of the Invention
This invention relates to dimensionally recoverable articles, particularly heat-recoverable articles, and to a method of installing such articles.
2. Introduction to the Invention
A dimensionally recoverable article is an article the dimensional configuration of which may be made substantially to change when subjected to treatment. Usually these articles recover towards an original shape from which they have previously been deformed, but the term "recoverable" as used herein, also includes an article which adopts a new configuration even if it has not been previously deformed.
A typical form of a dimensionally recoverable article is a heat-recoverable article, the dimensional configuration of which may be changed by subjecting the article to heat treatment. In their most common form, such articles comprise a heat-shrinkable sleeve made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in U.S. Pat. Nos. 2,027,962 (Currie); 3,086,242 (Cook et al); and 3,597,372 (Cook), the disclosures of which are incorporated herein by reference. The polymeric material has been crosslinked during the production process so as to enhance the desired dimensional recovery. One method of producing a heat-recoverable article comprises shaping the polymeric material into the desired heat-stable form, subsequently crosslinking the polymeric material, heating the article to a temperature above the crystalline melting point (or, for amorphous materials the softening point of the polymer), deforming the article, and cooling the article while in the deformed state so that the deformed state of the article is retained. In use, because the deformed state of the article is heat-unstable, application of heat will cause the article to assume its original heat-stable shape.
Recoverable articles are commonly used to cover objects, such as pipes or cables, having a tubular elongate configuration to provide, for example, environmental sealing protection. Where the diameter of the pipe is very large, thus making extrusion of a sufficiently large tubular sleeve difficult, or where no free end of the elongate object is available, it is common to use a wrap-around article, i.e. an article, typically in the form of a sheet, that is installed by wrapping it around the object to be covered so that opposed longitudinal edges overlap. A closure means is applied to secure together the opposed longitudinal edges of the wrap-around article. Such articles are described in U.S. Pat. Nos. 4,200,676 (Caponigro et al), 4,586,971 (Wallace), and 4,803,104 (Peigneur et al), the disclosures of which are incorporated herein by reference.
Recovery of the article is generally achieved by heat, e.g. from a torch, resistance wires, or other source. Such recovery can be craft-sensitive because it is necessary to heat the article sufficiently to recover it into contact with the substrate, but not so much that the article itself is damaged. In addition, if some or all of the surface of the article adjacent to the substrate is covered with an adhesive layer, it is necessary to heat the article enough to ensure that the adhesive layer is adequately heated and, for some adhesives, can flow. This can be difficult because the adhesive layer is usually covered by the article and thus is not visible for inspection. One common solution to this problem has been the use of a thermochromic paint on the outside of the heat-recoverable article. The paint is selected based on the nature of the article and the adhesive, if any, so that the paint changes color when adequate heat has been supplied. While such paint does allow the article to be inspected after recovery, the paint itself is expensive, must be applied using a solvent, and may produce "chalking" which is undesirable.
In another approach, described in U.S. Pat. No. 3,957,382 (Greuel, Jr. et al), the disclosure of which is incorporated herein by reference, a fusible insert which has protuberances on one surface is positioned between the substrate and the heat-recoverable sleeve. The protuberances are designed to prevent the sleeve from slipping out of position during installation. If the protuberance has a melting temperature similar to that of the insert, small bumps will be visible on the surface of the sleeve after recovery, indicating that the insert has been inadequately heated. This approach requires that a fusible insert be used and is not necessarily appropriate for use in systems without an insert.